Arachidonic acid activates cation channels in bovine adrenal chromaffin cells

Microscopic fluorescence analysis of fura-2-loaded bovine adrenal chromaffin cells demonstrates that approximately 70% of the cells responded to arachidonic acid in increasing the intracellular Ca2+ concentration. Because this increase was markedly less in the absence of external Ca2+, we examined the effect of arachidonic acid on Ca2+ influx electrophysiologically. Bath application of 10 microM arachidonic acid induced a long-lasting inward current when the cell was clamped at -50 mV. Other fatty acids, such as oleic acid, linoleic acid, eicosatrienoic acid, and eicosapentaenoic acid, were all ineffective. The current-voltage relationships suggest that arachidonic acid may activate voltage-insensitive channels. Arachidonic acid (> or = 2 microM) activated a single-channel current in the inside-out patch, even in the presence of inhibitors of cyclooxygenase and lipoxygenase, possibly suggesting that arachidonic acid could activate channels directly. The onset delay of the inward channel current in the outside-out patch configuration (54.2 +/- 63.5 s; mean +/- SD) was significantly shorter than that in the inside-out patch one (197.3 +/- 177.7 s). Washout of arachidonic acid decreased the probability of channel openings in the outside-out patch but not in the inside-out one. These results suggest that arachidonic acid activates channels reversibly from outside of the plasma membrane. The unitary conductance for Ca2+ of arachidonic acid-activated channel was approximately 17 pS. The arachidonic acid-activated channel was permeable to Ba2+, Ca2+, and Na+ but not to Cl-. The opening probability of the arachidonic acid-activated channel did not depend on membrane potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism and cardiovascular effects of leukotrienes in the marine toad Bufo marinus

Leukotriene (LT) metabolism and physiology have been studied extensively in mammals; however, little is known of their roles in nonmammalian vertebrates. This study examines the cardiovascular effects of leukotrienes on blood pressure and heart rate in the conscious and cannulated marine toad, Bufo marinus. The sulfidopeptide leukotrienes, LTC4, LTD4, and LTE4 elicited hypotension with equal potency. However, with respect to heart rate changes and duration of action, the responses to LTC4 and LTD4 were greater and lasted longer than those to LTE4. The nonpeptide leukotriene, LTB4, had significantly less potent effects on heart rate and blood pressure. The leukotriene-induced increases in heart rate with 1000 and 300 ng/kg body wt LTC4 and LTD4 were blocked with 5 mg/kg body wt propranolol, a beta-antagonist, suggesting sympathetic reflex regulation of heart rate. Metabolism of [3H]LTC4 to [3H]LTD4 and [3H]LTE4 occurred rapidly in blood, with complete conversion to [3H]LTE4 within 5 min. Conversion was slower in plasma, with 18.9 +/- 0.5% of the radioactivity associated with [3H]LTC4 still remaining after 120 min. The toad is more similar to mammals than the bullfrog with respect to the metabolism of leukotrienes. In contrast to mammals, leukotrienes have hypotensive effects in both toad and bullfrog, although the order of potency differs. The effectiveness of the sulfidopeptide leukotrienes in eliciting hypotension at low doses (1 ng/kg body wt) suggests that these compounds may be important cardiovascular regulators in the toad.

Glutamate uptake by astrocytes is inhibited by reactive oxygen intermediates but not by other macrophage-derived molecules including cytokines, leukotrienes or platelet-activating factor

By their property to release glutamate and reactive oxygen intermediates, macrophages may play an important role in neurotoxicity. In the present study we have investigated whether macrophage-derived molecules also impair the detoxification of glutamate by astrocytes. Cytokines, including interleukin (IL)-1, 6 and 10, interferon (IFN)-alpha/beta, tumor necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta 1, as well as leukotriene (LT) B4 and C4, prostaglandin (PG) E2 and nitric oxide radicals had no effect on the uptake of [3H]glutamate by murine astrocytes in culture. In contrast, exposure of astrocytes to the enzyme glucose oxidase (100-200 mU ml-1), which maintains steady-state levels of hydrogen peroxide, reduced glutamate uptake by 30-50%. By their dual effect, comprising secretion of glutamate and inhibition of its detoxification by astrocytes, activated macrophages and microglial cells may contribute to exacerbate excitotoxic mechanisms in neurological diseases.

Peptidoleukotrienes increase the efflux of glutathione from perfused rat liver

The effect of peptidoleukotrienes (LT) on the efflux of glutathione (GSH) from the perfused rat liver was investigated. LTD4, C4 and E4 were infused at a final concentration of 20 nM into the portal vein of rat livers perfused with Krebs-Henseleit buffer. Perfusion pressure, efflux of glucose and release of LDH increased during the infusion of LTC4 and D4 and returned to baseline upon cessation of the infusion of LT. In contrast, the efflux of GSH did not change during the infusion of LT, but increased from 15 +/- 2 to 26 +/- 4 nmol/min.g liver 20 min after cessation of the infusion of LTC4. LTE4 did not increase the efflux of LDH, glucose, lactate, or GSH. During the LTC4- and LTD4-induced rise in perfusion pressure bile-flow decreased transiently by one third. The biliary excretion of GSH, however, decreased by an average of 75% and recovered more slowly than the cholestasis. In the presence of the selective LTD4 receptor antagonist LY171883 the effects of LTC4 and LTD4 were largely abolished. The delayed effects of LT on GSH efflux suggest that LT shift the efflux of GSH from the canalicular towards the sinusoidal side of the hepatocyte independent of other effects of LT on hepatic function. The sustained increase in efflux of GSH resulting from LT will raise the extracellular concentration of this antioxidant, such that more GSH is available at sites of inflammation to detoxify reactive oxygen species released by activated inflammatory cells.

Ruptured erythrocytes inhibit the oxidation of membranes by 15-hydroperoxy-eicosatetraenoic acid

In this study, the pro-oxidant effects of the hydroperoxide, 15-hydroperoxy-eicosatetraenoic acid (15-HPETE), on erythrocyte membranes and the modulation of the oxidation by haem proteins released from ruptured erythrocytes have been assessed. The results indicate that ruptured erythrocytes may act as an antioxidant in protecting membranes against oxidative stress induced by hydroperoxides and that it is the oxyhaemoglobin that is the active constituent of the protective mechanism. An important feature of the mechanism is the peroxidatic action of oxyhaemoglobin and its rate of reaction with 15-HPETE.

Epidermal growth factor-induced actin remodeling is regulated by 5-lipoxygenase and cyclooxygenase products

In a number of cell types, epidermal growth factor (EGF) evokes dramatic morphological changes, cortical actin polymerization, and stress fiber breakdown. The molecular processes by which increased EGF receptor tyrosine kinase activity results in actin reorganization and morphological changes are unresolved. Recently, we demonstrated that arachidonic acid metabolites function in EGF signal transduction. We now report that in A431 cells, HeLa cells, and rat-1 fibroblasts, the EGF-induced cortical actin polymerization is produced by lipoxygenase metabolism, whereas in these cells stress fiber breakdown is mediated by cyclooxygenase metabolites. Also, the EGF-provoked rounding up in A431 cells is dependent on arachidonic acid metabolism. We conclude that leukotrienes and prostaglandins act in concert, as second messengers, to produce morphological effects and actin reorganization, providing a novel mechanism for directing growth factor-induced cytoskeletal changes.

Modulation of acetylcholine release from the myenteric plexus of guinea-pig ileum by 5-lipoxygenase metabolites of arachidonic acid

Eicosatetraenoic acid, an inhibitor of 5- and 12-lipoxygenase, and AA861, a selective inhibitor of 5-lipoxygenase, dose dependently inhibited acetylcholine release from the myenteric plexus of guinea-pig ileum induced by electrical field stimulation. Metabolites of arachidonic acid produced by the 5-lipoxygenase pathway, such as 5-hydroxyeicosatetraenoic acid (5-HETE), leukotriene C4, D4 and E4, reversed the inhibitory effect of AA861. Among them, leukotriene D4 was the most potent, having an EC50 value of about 3 nM. The present study shows for the first time that 5-lipoxygenase metabolites may have a modulatory effect on acetylcholine release in the myenteric plexus of guinea-pig ileum.

Independent arachidonic acid-mediated gene regulatory pathways in lymphocytes

In the BW5147 T cell line, we have identified two independent regulatory pathways by which arachidonic acid (20:4) can alter gene expression. The inhibitory effect of 20:4 upon stearoyl-CoA desaturase 2 (SCD2) gene expression was seen to be independent of oxidation of 20:4 by either the lipoxygenase or cyclooxygenase pathways. Moreover, oxidized metabolites of 20:4 (15-HPETE and 15-HETE) failed to diminish SCD2 mRNA accumulation whereas 20:4 itself was effective in completely suppressing SCD2 gene expression. In contrast, the transcriptional induction of the proto-oncogene c-fos was dependent upon the oxidation of 20:4 by the lipoxygenase pathway. By using the protein synthesis inhibitor, cycloheximide, we also show that the 20:4-mediated regulatory effects upon SCD2 or c-fos are completely independent of new protein synthesis. Collectively, the results identify the existence of multiple, independent, intracellular 20:4-mediated regulatory pathways operating simultaneously within this cell type.

Characterisation of the peptido-leukotriene receptor PL2 on the ferret spleen strip

The peptido-leukotriene receptor(s) (PL) on the ferret isolated spleen strip have been characterised by functional studies using the naturally occurring leukotrienes (LTs), a range of structurally distinct PL antagonists, and by ligand binding studies. LTB4 (0.01-10 microM) was inactive on ferret spleen whereas LTC4, LTD4 and LTE4 produced concentration-related contractions with maximal responses, relative to noradrenaline, of 57% (EC50 0.28 microM), 60% (EC50 0.5 microM) and 7% respectively. The leukotriene responses were unaltered by L-serine borate, L-cysteine, indomethacin, phentolamine, propranolol, mepyramine, methysergide or atropine, suggesting that the peptido-leukotrienes were acting through distinct PL receptors. The PL1 antagonists, FPL 55712 (0.01-10 microM), ICI 198615 (10 microM), SK&F 104353 (10 microM) and MK541 (10 microM) were all inactive against LTC4- or LTD4-induced contractile responses. LTE4 was a partial agonist with respect to LTC4 and LTD4 with pKB values of 5.8 and 5.5 respectively. Nifedipine (0.1 microM) produced a rightward shift of the concentration-response curves to both LTC4 and LTD4 and depressed their maximal responses. An unacceptably high level of non-specific binding of [3H]LTD4 to membrane preparations of ferret spleen prevented characterisation of this receptor by ligand binding. These results suggest that the ferret spleen has a homogeneous population of a PL receptor type which is insensitive to existing PL1 receptor antagonists. The functional characteristics of this PL receptor type are similar to those of the PL2 receptor on other tissues. The absence of PL1 receptors on this tissue makes it particularly useful in identifying new and selective drug tools for the PL2 receptor.

The influence of an PGF2x analogue and of some peptidoleukotrienes and platelet activating factor antagonists in experimentally induced gastric ulcer in rats

We tested the influence of 30 mg/kg/per os BN 52021, 300 micrograms/kg Cloprostenol (CIPG) and of 5 mg/kg per os LY 171883B in stress restrain and indomethacin induced ulcers in rats. The data obtained show that CIPG and LY 171883 have a significant gastroprotective action in both ulcer models. BN 52021 has a significant protective activity in stress ulcer and less in indomethacin-induced ulcers.

Identification and target-size analysis of the leukotriene D4 receptor in the human THP-1 cell line

The human acute monocytic leukemia cell line THP-1 has been identified, by radioligand binding, as expressing the leukotriene D4 receptor at a high level (4000 binding sites per cell), without the need for further cell differentiation. [3H]Leukotriene D4-specific binding to THP-1 cell membranes was of high affinity (KD = 0.47 nM) and saturable, enhanced by divalent cations but inhibited by both monovalent cations and non-hydrolyzable GTP analogs. The cysteinyl leukotrienes competed for [3H]leukotriene D4-specific binding with the following rank order of potency: leukotriene D4 >> leukotriene E4 > leukotriene C4. In addition, leukotriene D4-receptor antagonists from two structural classes, the quinolines MK-571 and L-697,008, and the indole ICI 204,219, displayed nanomolar potency in [3H]leukotriene D4 competition assays. These data show that [3H]leukotriene D4-specific binding to THP-1 cell membranes fulfils the criteria for binding to a leukotriene D4 receptor regulated through interaction with a G protein. Several novel features of the THP-1 leukotriene D4 receptor were investigated. Culture of THP-1 cells in the presence of tunicamycin, an inhibitor of N-glycosylation, resulted in a 6-fold decrease in the number of detectable [3H]leukotriene D4-specific binding sites. Target-size analysis by radiation inactivation estimated a molecular mass of 65 kDa for the [3H]leukotriene D4 specific binding site(s) present in THP-1 cell membranes. Together, these results suggest that the human THP-1 cell leukotriene D4 receptor is a glycosylated protein with a molecular mass of approx. 65 kDa within the membrane environment.

Possible radical scavenging properties of cicletanine and renal protection in Dahl salt sensitive rats

Much interest in cicletanine, a novel antihypertensive drug, has grown because it uniquely stimulates prostacyclin (PGI2) production and may, thereby, provide further cardiovascular protection. We postulated that cicletanine may be an antioxidant, and assessed its ability to protect the kidney in Dahl salt-sensitive (Dahl S) rats on a high salt diet. Cicletanine eradicated in vitro a stable radical, DPPH, and decreased the lipid peroxidation both in rat brain homogenate and in a xanthine-xanthine oxidase (X-XOD) superoxide generating system. Furthermore, cicletanine attenuated the inhibition of PGI2 synthase activity by 15HPETE. However, cicletanine did not exhibit superoxide dismutase-like activity in X-XOD system, suggesting that it behaves primarily as a hydroxy radical scavenger. A 6 week cicletanine treatment reduced blood pressure in Dahl S rats fed a high salt diet, and ameliorated functional and morphological injury to the kidney. This attenuation of glomerular sclerosis correlated with the attenuation of lipid peroxidation in the kidney homogenate. These data indicate that cicletanine is an antioxidant that protects the kidney from salt-induced hypertension in Dahl salt-sensitive strain rats.

5-Lipoxygenase metabolites of arachidonic acid stimulate isolated osteoclasts to resorb calcified matrices

Bone resorption requires cooperation between osteoclasts and mononuclear accessory cells by mechanisms which have not been elucidated. Since multinucleated cells in giant cell tumors of bone have many phenotypic and functional characteristics of normal osteoclasts, we have examined the interaction between the bone-resorbing multinucleated cells and the distinct mononuclear stromal cells from these tumors. We have found that these mononuclear cells produce an activity which stimulates both giant cells from giant cell tumors and rodent osteoclasts to resorb bone in vitro. We have identified the activity and found that it represents several products of the 5-lipoxygenase pathway of arachidonic acid metabolism, namely 5-hydroxyeicosatetraenoic acid and the leukotrienes. These data indicate that 5-lipoxygenase metabolites stimulate isolated osteoclasts to resorb bone in vitro and may represent a mechanism by which mononuclear stromal cells in human giant cell tumors communicate with the giant cells. In addition, these results may explain a possible mechanism for communication between accessory cells and osteoclasts involved in normal bone resorption.

Effect of leukotrienes on sheep airway smooth muscle

The effects of leukotrienes (LT) C4, LTD4, LTE4 and LTB4 on the development of isometric tension by sheep airway smooth muscle were determined in a tissue bath. LTE4 (1.5 x 10(-7) M) had no contractile effect. LTB4 contracted only lung parenchymal strips. LTC4 (8 x 10(-8) M) and LTD4 (1.1 x 10(-7) M) caused contractions in trachea, bronchi and lung parenchyma that developed slowly and persisted. The tracheal contractions caused by LTD4 and ACh were potentiated approx. 30% by the cyclooxygenase inhibitor meclofenamate (10(-6) M). Meclofenamate had no effect on leukotriene induced contractions in bronchi or lung parenchymal strips. The bronchodilator prostaglandins PGI2 and PGE2 were released from sheep trachea at rest and after contraction by LTD4. Inhibition of their release by meclofenamate may explain the potentiation of LTD4 contractions by meclofenamate. In vitro, LTD4 and LTC4 have potent contractile effects on sheep airway smooth muscle that are not mediated by the secondary release of constrictor cyclooxygenase products. These leukotrienes may play a substantial role in the pathogenesis of allergen and endotoxin induced lung mechanics changes in sheep.

Influence of arachidonic acid on indices of phospholipase A2 activity in the human neutrophil

The present studies were conducted to understand better the regulation of phospholipase A2 (PLA2)-dependent mobilization of lipid mediators by arachidonic acid (C20:4). After stimulation of human neutrophils, g.l.c./m.s. analysis of non-esterified fatty acids indicated that the quantity of C20:4 increased as a function of time after stimulation, from undetectable quantities to > 800 pmol/10(7) cells. In contrast with C20:4, the quantities of other free fatty acids such as oleic and linoleic were high in resting cells and did not change after stimulation. Some 15% of the C20:4 released from cellular lipids remained cell-associated. To examine the effect of C20:4 on its own release, neutrophils were exposed to [2H8]C20:4, to differentiate it by g.l.c./m.s. from naturally occurring C20:4. In A23187-stimulated neutrophils, low concentrations (5-10 microM) of [2H8]C20:4 added just before A23187 increased the quantity of C20:4 produced by the cell, whereas higher concentrations (30-50 microM) decreased the quantity of C20:4 released from phospholipids. As other measures of PLA2 activity, the effects of C20:4 on production of platelet-activity factor (PAF) and leukotriene B4 (LTB4) were assessed. C20:4 treatment just before stimulation of neutrophils blocked PAF and LTB4 production in a concentration-dependent manner (IC50 10-20 microM). The effect of C20:4 was not blocked by the cyclo-oxygenase inhibitor naproxine (10 microM), nor could it be mimicked by 1 microM LTB4, 5-hydroxyeicosa-6,8,11,14-tetraenoic acid (5HETE), 5-hydroperoxyeicosa-6,8,11,14-tetraenoic acid (5HPETE) or 15-hydroxyeicosa-5,8,11,13-tetraenoic acid (15HETE). The 5-lipoxygenase (5LO) inhibitor zileuton induced a concentration-dependent decrease in PAF, with a maximal effect of a 50% decrease at 10-50 microM. The decrease in PAF by the 5LO inhibitor could not be circumvented by addition of 1 microM 5HETE, 5HPETE and LTB4, and may be attributed to the capacity of zileuton to increase the quantity of C20:4 in A23187-treated neutrophils. The inhibitory effect of C20:4 (20-40 microM) on PAF production could be antagonized by the protein kinase C inhibitor staurosporine (30 nM), but not by inhibitors of protein kinase A, tyrosine kinase or calmodulin kinase II. Taken together, these data demonstrate that C20:4 is selectively released from membrane phospholipids of A23187-stimulated neutrophils, and this C20:4 may play an important role in regulating the mobilization of C20:4 by altering PLA2 activity.

Regulatory effect of arachidonic acid on the calcium transport system in rat liver nuclei

The effect of arachidonic acid (AA) on Ca2+ transport in rat liver nuclei was investigated. Ca2+ uptake and release were determined with a Ca2+ electrode. Ca2+ uptake increased dependent on ATP (0.5-2.0 mM), while uptake was negligible in the presence of 2.0 mM ADP or AMP. AA (10-100 microM) caused a marked inhibition of Ca2+ uptake following the addition of 2.0 mM ATP. Also, Ca2+, which accumulated in the nuclei during 6 min after ATP addition, was clearly released by the addition of AA (10-100 microM). The alterations were concentration dependent. The nuclear Ca2+ uptake and release were not altered significantly by the presence of prostaglandin E2 (10 and 20 microM), prostaglandin H2 (1 and 4 microM), thromboxane B2 (1 and 4 microM), leukotriene A4 (1 and 4 microM), Ins(1,4,5)P3 (1 and 10 microM) or dibutyryl cAMP (10 and 50 microM). Only, 5-hydroxy-eicosatetraenoic acid (5-HETE) at 4 microM caused a significant inhibition of nuclear Ca2+ uptake and an appreciable increase in Ca2+ release; the 1 microM concentration had no effect. These results indicate that AA, one of the prostanoids, has a unique effect on Ca2+ uptake and release in rat liver nuclei. The finding suggests that AA has a regulatory effect on the Ca2+ transport system in liver nuclei.

Differential effects of 15-HPETE and 15-HETE on BHK-21 cell proliferation and macromolecular composition

Arachidonate and/or linoleate metabolites have been implicated in modulating cell growth, replication and cell transformations. In studies with BHK-21 cells, we found lipoxygenase and cyclooxygenase inhibitors (NDGA and indomethacin, respectively) to be antiproliferative. Studies on the metabolism of arachidonic acid in BHK-21 cells have demonstrated that prostaglandin D2 is the major cyclooxygenase product, and 15-hydroxyeicosatetraenoic acid (15-HETE) is the major lipoxygenase product. Addition of D2 showed a significant decrease in the BHK-21 cell number showing antiproliferative action. Addition of lipoxygenase products, on the other hand, showed differential effects in that 15-HPETE decreased the cell number while 15-HETE increased. NDGA and 15-HPETE decreased DNA, RNA and protein contents, while 15-HETE significantly increased them. 5-HPETE and 5-HETE also showed similar results but were less potent than 15-H(P)ETEs. The differential effects of 15-HPETE and 15-HETE could be due to the generation of free radicals by the hydroperoxide and mitogenic response by hydroxide.

Effect of nedocromil sodium on sulfidopeptide leukotrienes-stimulated human alveolar macrophages in asthma

Alveolar macrophages (AM) may take part in the amplification of the inflammatory mechanism involved in asthma. During an asthma attack, mast cells and eosinophils release arachidonic acid derivative mediators of inflammation such as sulfidopeptide leukotrienes. Among them, LTC4 has been shown to be present in bronchoalveolar fluid. In asthmatic patients, we showed that the ability of AM to transform LTC4 into its derivatives LTD4 and LTE4 was related to the intensity of the local inflammation observed during endoscopy. AM from asthmatics incubated in the presence of LTC4 or LTE4, generated LTB4 and 5-HETE, which are potent chemoattractants. Nedocromil sodium (10(-4) M) decreased LTB4 releasability and intracellular 5-HETE concentrations in zymosan-stimulated AM from asthmatic patients, and was shown to decrease the LTC4 or LTE4-promoted formation of LTB4 and 5-HETE.

Leukotrienes and histamine mediate IgE-dependent contractions of human bronchi: pharmacological evidence obtained with tissues from asthmatic and non-asthmatic subjects

Isolated human bronchi were challenged with anti-human IgE or specific allergen. The mediators of allergic constriction were characterized by pharmacological interventions. Experiments were performed on more than 180 preparations obtained from 48 non-asthmatic subjects and on 44 bronchial preparations from six asthmatic subjects. Addition of antihistamines (mepyramine and metiamide) to the organ bath abolished the response to exogenous histamine, but failed to alter the dose-response relationship of the reaction to cumulative challenge with rising titres of anti-IgE. On the other hand, pretreatment with drugs which blocked the action (receptor antagonists FPL55712, L-648,051 and ICI 198,615) or formation (biosynthesis inhibitors: U-60,257 and MK886) of leukotrienes consistently resulted in clear-cut inhibition of the allergic constriction in bronchi from both asthmatic and non-asthmatic subjects. In the presence of the most effective inhibitors (ICI 198,615 and MK886), the response to anti-IgE was depressed by more than 60%. In contrast, the cyclooxygenase inhibitor indomethacin and the antagonist of platelet activating factor (PAF) WEB 2086, failed to alter the response, indicating that prostanoids and PAF do not mediate IgE-dependent constriction of human bronchi. After the leukotriene antagonist ICI 198,615 had rendered the bronchi insensitive to exogenous leukotrienes, the residual component of the contractile response to anti-IgE was completely abolished by addition of antihistamines. Similar abolition of the Schultz-Dale reaction in bronchi of two allergic asthmatic patients was noted when antihistamines were administered together with ICI 198,615 or MK886. In conclusion, the leukotrienes appear to be the major and singularly most important mediators of the contraction, whereas histamine accounts for its minor residual component.

Formation and effects of leukotrienes and lipoxins in human bone marrow

The present results demonstrate leukotriene and lipoxin synthesis in human bone marrow and link these findings to biological effects in the same tissue. However, the mechanisms behind the described effects on myeloid progenitor cell growth are presently unknown. It is conceivable that both leukotrienes and lipoxins may act through modulation of endogenous cytokine production. However, it should be noted, that these lipoxygenase products totally failed to induce colony growth in the absence of GM-CSF. Moreover, the role of lipoxins in the bone marrow needs to be further clarified, since LXA4 induced both synergistic (with GM-CSF) and antagonistic (with LTC4) effects on progenitor cell growth. A possible pathophysiological role for leukotrienes and lipoxins may be suggested in chronic myelogenous leukemia. Thus, the capacity of hematological cells from CML patients to synthesize LTC4 was significantly increased. In addition, we have recently reported that CML platelets possessed a markedly decreased ability to participate in transcellular synthesis of the potential inhibitors of myelopoiesis, LXA4 and 5(S),12(S)-diHETE (Stenke et al., 1991b). Moreover, the production of these compounds was totally abolished in platelets obtained from CML patients in blastic crisis. Further studies should aim at defining the mechanisms behind the regulatory actions of leukotrienes and lipoxins in normal and leukemic human myelopoiesis.

Vascular interaction between 5-hydroxytryptamine and 15-lipoxygenase metabolites of arachidonic acid

In isolated canine saphenous veins, the contractions elicited by the 15-lipoxygenase metabolites 15-HETE and 15-HPETE were augmented by 5-hydroxytryptamine (5-HT) in a concentration-dependent way. This potentiation was not mediated by the endothelium nor was it influenced by the 5-HT2-antagonist ketanserin. Phentolamine, however, reduced both the contractions and the potentiation by 5-HT. These data provide evidence for a receptor-mediated potentiation by 5-HT which occurs independently of 5-HT2-receptors. The interaction between 5-HT or aggregating platelets and 15-HPETE was studied in isolated rabbit brachiocephalic arteries. Threshold concentrations of 5-HT and platelets markedly potentiated the contractions elicited by 15-HPETE. In brachiocephalic arteries obtained from cholesterol-fed rabbits, 15-HPETE, 5-HT and platelets caused contractions similar to those obtained in control rabbits. The potentiating effect of 5-HT and platelets on the 15-HPETE-induced contractions was also comparable to that observed in control rabbits. Moreover, no difference was found between control platelets and platelets obtained from hypercholesterolemic rabbits. Our findings demonstrate a positive interaction between 5-HT and 15-lipoxygenase metabolites of arachidonic acid in arteries and veins. This interaction persists in atherosclerotic arteries and could indicate that this mechanism is involved in the genesis of vasospasm.

In vitro changes in the properties of rabbit colonic muscularis mucosae in colitis

BACKGROUND

The muscularis mucosae is the muscle layer closet to the site of elevated inflammatory mediator production in inflammatory bowel disease. Thus, it is the first muscle layer subject to their influence.

METHODS

Using a rabbit trinitrobenzene sulfonic acid model of colitis, changes in the properties of the muscularis mucosae resulting from the inflammatory process were studied in vitro.

RESULTS

Animals developed a mild colitis-like inflammation that was confined to the epithelium, lamina propria, and submucosa. Colitic muscularis mucosae contractile responses to leukotriene D4 and prostaglandins E2 and F2 alpha were significantly attenuated relative to the maximum tissue response to acetylcholine, whereas responses to histamine, substance P, and vasoactive intestinal polypeptide were unchanged. In addition, the stress-generating capacity of the colitic muscularis mucosae was compromised in a stimulus-independent manner and passive tension increased relative to active tension.

CONCLUSIONS

The muscularis mucosae undergoes two significant alterations in colitis: (a) a selective desensitization to the effects of arachidonic acid metabolites and (b) an impairment of its excitation-contraction coupling mechanism. A loss of the ability of the muscularis mucosae to cause mucosal movement and alter luminal surface area may be an important early stage in the pathophysiology of inflammatory bowel disease.

cAMP-specific phosphodiesterase inhibitor, rolipram, reduces eosinophil infiltration evoked by leukotrienes or by histamine in guinea pig conjunctiva

The effect of rolipram, an isozyme IV-selective inhibitor of cAMP-specific phosphodiesterase, was evaluated in a guinea pig eye model of tissue eosinophilia. (R)-rolipram was administered by gavage to guinea pigs 1 h prior to topical ocular challenge with a mixture of leukotrienes (LTs) (10 ng LTB4 + 1000 ng LTD4/eye) or with histamine dihydrochloride (1 mg/eye). Conjunctivae were evaluated histologically 6 h after challenge. Eosinophil counts per millimeter of conjunctival epithelium in LT-challenged animals that received (R)-rolipram at dosages of 0.1, 0.3, 1, 3, or 10 mg/kg were reduced by 63, 63, 84, 81 and 90% respectively, compared to LT-challenged controls. Reduction was statistically significant (P < 0.05) at all dosages. Eosinophil counts per millimeter of epithelium in histamine-challenged animals that received 10 mg/kg (R)-rolipram were reduced by 79% compared to histamine-challenged controls (P < 0.01). The results indicate that (R)-rolipram inhibits the response to two distinct classes of mediator in this model of eosinophil infiltration, adding support to the contention that isozyme IV-selective cAMP phosphodiesterase inhibitors offer therapeutic potential for human asthma.